In youngs double slit experiment, does the wavelength of a light affect its brightness? If it increases, does the brightness change?

Wavelength is proportional to the energy of each photon. Brightness is related to the number of photons. They are two different concepts.

Practically no, really yes, it depends, let's say yes. It needs a tighter question really.

Brightness isn't a well defined term here. If you use one source with wavelength A and then a different source with wavelength B and make the power the same, then by definition the radiant energy is the same (radiometric - brightness as real physical energy) but there may be change in luminous energy (photometric - brightness as it appears to the human eye). However, if A and B are both well inside the visible light range the perceived difference will not change too much anyway because the full spectrum of visible light is actually quite narrow, less than two octaves.

If you consider the full EM spectrum and you consider photons of light (an ironic thing to do!) then the wavelength of one photon is inversely proportional to radiant energy.